1. Field of the Invention
The present invention relates to an image sensing apparatus and a control method for the image sensing apparatus, and more particularly, to an image sensing apparatus with an electronic viewfinder function.
2. Description of the Related Art
In a single-lens reflex camera that is one type of image sensing apparatus, when observing an object using an optical viewfinder (OVF), light beams exiting from a photographing lens are reflected by a mirror provided on an image plane side of the photographing lens and directed to an optical viewfinder that includes a pentaprism or the like. Such an arrangement enables a photographer to see an image of an object formed by the photographing lens as a normal image. At this time, the mirror is set obliquely in the photographic optical path. To photograph an image of an object from this state, the mirror is momentarily withdrawn from the photographic optical path to allow the light beams from the photographing lens to reach an image sensor. Then, when photography is finished, the mirror is immediately returned to its original position in the photographic optical path.
By contrast, as another method of observing an image of an object there is an electronic viewfinder (EVF), which reads out a reduced resolution image signal of the image of the object from the image sensor and displays the read-out image signal on a display unit such as an LCD mounted on a rear side of the camera, at a high display rate and in real time. In this case, the mirror is withdrawn from the photographic optical path and the shutter is kept open so as to direct light beams exiting from the photographing lens to the image sensor without blocking the light beams (see, for example, Japanese Patent Application Laid-Open No. 2006-33705).
The display unit provided on the rear surface of the camera is usually configured so as to be able to carry out displays suitable for multiple purposes, such as displays of information set in the camera, menus to change the set functional contents, photographed images, and the like. In addition, switching of the display on the display unit is user selectable. When an image other than the image of the object (such as a menu screen) is selected while in the EVF mode for viewing the object with the electronic viewfinder, the display is immediately switched from a screen showing the image of the object to the menu screen.
When the menu screen is displayed in the EVF mode, as described above the camera withdraws the mirror from the photographic optical path and keeps the shutter open so that the light beams exiting from the photographing lens can be directed to the image sensor without being blocked. However, because the menu screen is being displayed, the user cannot see the image of the object that is entering the image sensor. As a result, for example, if the photographing lens is inadvertently pointed toward the sun, sunlight is then focused on the image sensor, possibly causing a portion of the image sensor to heat up and burn out.
If the mirror is moved every time there is a switch to the menu screen, the sound of the mirror moving, and especially the sound of impact as the mirror descends into place, not only is noisy but can also mislead the user into thinking that the shutter release button has been pressed. In addition, when returning from display of the menu screen to the EVF display screen to once again display an image of the object, because the mirror has to be driven it takes longer to return to the screen showing the image of the object, which is inconvenient.